According to the present state of the art, ovens are already known in which the products are inserted and removed on an open trolley. The trolley inserted into the oven is generally rolled on to a disc which is rotated and disposed at the level of the floor of the baking chamber. In these ovens, the products are baked by a jet of hot air injected constantly through apertures in the side of the baking chamber. This hot air jet is induced, for reheating and recirculation, through apertures in the opposite side of the baking chamber. It thus happens that the air stream deriving from the jet of hot air traverses the trolley from one side to the other horizontally, while the trolley, after being placed on the disc and after the oven door has been closed, is slowly rotated by way of the floor disc, which is driven by a motor so that the trolley rotates about a vertical axis.
Thus, the products disposed on each shelf are baked equally at all points of the rectangle represented by each shelf.
However ovens using this known method for equalising the heat have various drawbacks, particularly having regard to their overall size and energy consumption. In this respect, the inner volume of the baking chamber is more than double the utilised volume represented by the parallelepiped generated by the trolley rotating about its vertical axis. This doubling of the internal volume of the baking chamber is due to the fact that the base of the baking chamber is essentially square, owing to the fact that it contains the rotating disc on which the substantially rectangular base of the trolley is inscribed.
This volume doubling leads to an unprofitable excess energy consumption, which is used on the one hand for raising the initial temperature of the oven, and on the other hand for filling the oven with steam as is necessary at the commencement of baking of each batch of products to be baked.
In addition, the presence of the disc rotating in the base of the baking chamber, and the fact that it is close to the ground in order to prevent the need for the trolley access ramp to be too steep, make correct heating and insulation of the base difficult.
A batch baking oven with hot air control for baking bakery products disposed on an open trolley is also known from U.S. Pat. No. 3,529,554. Baking is performed by a hot air stream supplied to the baking chamber through a plurality of air jets. The baking chamber comprises two parallel walls with a plurality of vertical slots separated from each other. These walls serve as separation elements between an outer chamber and the baking chamber. The two parallel walls are subjected to a reciprocating movement, and the slots move in parallel vertical planes.
According to one modification, the parallel walls are immobile, and with each vertical slot there is associated an injector formed from two vertically extending spaced flat parallel plates. Between the two flat plates there is disposed a roller mounted on a vertical shaft subjected to a reciprocating movement by way of a horizontal connection bar.
In a second modification, the parallel walls comprise vertical seats in which vertical bars having a vertical slot are disposed. One end of each bar is fitted with an horizontal arm connected by a vertical pivot to a connection bar subjected to reciprocating movement.
A rotary sweeping of hot air jets is obtained only with these two modifications.
However, this oven has numerous drawbacks. In this respect, the various means used, namely the slots provided in the mobile walls, the flat plates extending vertically along the slots provided in the fixed walls, and the rotating sets provided with a vertical slot serve only as a passage for the hot air arriving from the outer chamber, by diffusing it into the baking chamber. It is therefore necessary firstly to fill the outer chamber before the hot air can penetrate into the baking chamber. The hot air is blown by a fan, and because of the large volume necessary for filling the outer chamber, the throughput of this hot air fan has to be enormous. To obtain this throughput, it is necessary to incorporate into the oven a fan of such power that it becomes incompatible with the oven.
Moreover, the hot air circulating through the outer chamber must have a pressure sufficient for its passage through the various means in the direction of the baking chamber. The flow rate of each stream of air is very low because this flow is divided among a plurality of slots. Thus, the direction of each stream is only determined in the immediate proximity of the outlet of each slot. Because of this, the products situated in a central position in the baking chamber are not sufficiently heated.